1. Field of the Invention
The present invention relates to a method of transmitting data using adaptive coding scheme, which changes channel coding rate of transport blocks (TBs) adaptively in accordance with channel transmission conditions, at physical layer of asynchronous mobile communication system such as W-CDMA or IMT-2000 in order to achieve effective data transmission, and relates to a base station using said method.
2. Description of the Related Art
For next generations of mobile communication system, standardization on synchronous and asynchronous system is going on. Related companies participate actively in the standardization to prepare for changes and trend of mobile communication technology.
The synchronous mobile system has been adopted in United States and some countries while major communication companies in Europe, Japan, Korea, and United States are participating in the standardization of asynchronous mobile system. Therefore, it is expected that asynchronous system of IMT-2000 will be main stream in the mobile communication system.
In the standardization of asynchronous mobile system of IMT2000, basic scheme has been completely set, however, optional standard for various supplementary functions is still under discussion at present. For such supplementary functions, technology on hybrid Automatic Retransmission Request (ARQ) and high-speed packet data transmission is under consideration in the optional standardization on wireless interfacing layers of asynchronous IMT-2000 system.
The two technologies aim at reducing transmission time and maximizing transmission efficiency of channels. In the field of hybrid ARQ, methods and procedures on transmitting additional information and soft combination are under discussion, and, in the field of high-speed packet data transmission, mechanisms about quick recovery from failure are under discussion. The two technologies are being standardized to resolve different issues, however, they have substantial common objective of maximizing transmission efficiency of packet data.
In the technique of hybrid ARQ, a puncturing rate is adjusted at transmission rate matching process to apply type II/III. The amount of substantial data being transmitted per a given time through a physical layer changes in proportion to the adjusted puncturing rate. At initial transmission, the puncturing rate is set to high, however, it is lowered as data retransmitted times are increased.
Applying hybrid ARQ, data delivery is guaranteed in good channel even if relatively small amount of data is transmitted, which improves efficiency of physical channel utilization. In addition, a receiving part stores transport blocks which contain errors in a buffer instead of discarding them, and combines the stored error-containing blocks with same blocks which are retransmitted with lower puncturing rate, therefore, errors will be reduced.
If errors occurs at radio link control (RLC) layer, it will take relatively long time to recover erroneously received blocks, which means reduction of transmission efficiency. Therefore, researches into retransmission mechanism is progressive in the high-speed packet data transmission service to resolve such a delay problem. These researches include a method of transmitting acknowledge information at physical layer for each data unit sized by transport time interval (TTI).
As aforementioned, the two techniques have common objective of improving efficiency of data transmission, therefore, it is preferable to combine the two techniques, namely, to apply the method of transmitting acknowledge information at physical layer to the hybrid ARQ, or to apply the hybrid ARQ to the high-speed packet data transmission service. If the two techniques are combined, then, more effective data transmission will be achieved.